In Iowa's Corn and Bean Fields, Clues to Jet Crash

By JOHN H. CUSHMAN Jr., Special to The New York Times

Published: July 25, 1989

SIOUX CITY, Iowa, July 24—
Somewhere in the shaded furrows of knee-deep soybeans and towering corn in western Iowa may lie the solution to the mystery of why a United Airlines jumbo jet crashed here last Wednesday.

Three critical pieces of the jet's tail-mounted engine, which came apart at 30,000 feet about 60 miles east of here, are still missing, and investigators say they must be found to deduce why the engine failed.

Robert MacIntosh, the National Transportation Safety Board's investigator in charge, said that search parties had found a few pieces of aircraft wreckage today, but that ''the parts that we have not recovered are the parts that we are very interested in.''

The most important missing part is the engine assembly's disk, a heavy metal part with gearlike teeth on its outer rim. It is about three feet in diameter. Another Passenger Dies

As the search for clues continued today, United Airlines reported that a passenger on the flight, Brent Bealer of Quakertown, Pa., had died in the hospital of injuries from the crash. That raised the number of fatalities to 111, of whom 108 have been positively identified. The number of confirmed survivors is now 185. Thirty-eight of the survivors remain hospitalized.

Members of the Air National Guard from Iowa and Nebraska are conducting the search for missing parts and are concentrating on a 16-square-mile area in which the aircraft's tail cone and a few pieces of the engine assembly have already been found. They are using helicopters and night-vision cameras mounted on Phantom reconnaissance jets.

Although some ground searches have been attempted, that approach seemed so fruitless in the dense foliage that it has now been suspended until the aerial search provides some glimmer of evidence about where the debris may lie. Some investigators are beginning to wonder whether the engine's remnants will remain concealed until farmers bring in their crops in the late summer or early fall.

The missing parts include blades from the forward fan section of the engine, the metal disk to which the fan was attached and part of the shaft on which the assembly spins during flight.

Investigators hope that by closely examining these parts, metallurgists in the safety board's laboratory will be able to tell which part was first to give way and whether the failure was due to improper maintenance, a flaw in the manufacturing process or metal fatigue caused by repeated stress or by some sudden force. Examining Parts and Documents

While they searched for the missing parts, investigators continued today to examine parts of the DC-10 aircraft's wreckage. The tail section - where debris from the disintegrating engine appears to have damaged vital hydraulic lines and made the plane virtually uncontrollable - was moved into a hangar at the airport for further inspection.

At United's San Francisco maintenance headquarters, investigators combed through thousands of documents about the plane's mechanical history. No significant findings were reported by a board spokesman here.

Safety board officials said tonight that investigators are going to Cincinnati, where the engine was made by General Electric, to examine the manufacturing history of the disk and other engine parts.

The search for the missing engine parts is taking place in territory almost entirely covered by crops. The area is about 12 miles northwest of Alta, Iowa.

The transportation safety board used a computer to calculate the probable location of the parts, based on information about when and where the engine failed, the speed and altitude of the plane, the winds at the time, the probable weight and aerodynamic characteristics of the missing parts and the locations of the parts already found in the area.

Each evening two RF-4 reconnaissance planes of the Nebraska Air National Guard have taken pictures of the area using infrared cameras, which detect the heat of objects on the ground.

But the infrared cameras may not be able to penetrate the cover of broad leaves of soybeans and corn.

The fan blades from the engine are several feet long. Thirty-eight of them were in the assembly that broke loose from the plane, but many probably broke off in the accident. More important to investigators are the disks to which the fans were attached and the rotating shaft that spun the disks.

The engine contained two disks. All of the stage one disk, closest to the front of the engine, is missing, and part of the stage two disk is also missing.

Information obtained by investigators from United's records shows that the stage two disk had been used on 16,723 flights; the normal limit is 17,000 flights. The stage one disk had been on 15,503 flights, and its limit is 18,000, safety board officials said.